The present invention relates to methods and devices for thermally treating metal wires. Such methods and devices permit, for instance, the perlitization of steel wires so as to obtain a fine perlitic structure at a high speed, for instance at least equal to 15 m/second.
From SU Patent A-1 224 347, it is known to effect a perlitization treatment by passing a steel wire over smooth capstans placed in the ambient air so as to effect this treatment at a substantially higher speed than in a conventional lead patenting installation and without having the drawbacks of said lead technique which reside, in particular, in the dangers to health and the protection of the environment. Experience shows that the method described in that patent leads to the obtaining of products having a definitely poorer value in use than that which can be obtained with lead patenting. As a matter of fact, the cooling curve contains a substantial area of recalescence, for example a rise in temperature of 50.degree. C. for wires having a diameter of 3 mm. This substantial recalescence is due to the poor heat transfer coefficient between the wire and the capstan, which leads to a large difference in temperature between the wire and the capstan when the thermal power peak caused by the transformation of austenite into perlite takes place. Now, the presence of recalescence above 20.degree. C. during the heat treatment does not make it possible to obtain a high value in use of the wires, particularly when they are of large diameters.
European Patent Application A-275 864 describes a method for the heat treatment of metal wires by passing them over disks having grooves within an enclosure in which a protective gas is contained, the heating of the wires being obtained directly by irradiation.
U.S. Pat. No. 2,965,368 describes a method for the heat treatment of metal wires by passing them through grooves of capstans which are heated on the inside, the wires being reeved crosswise on these capstans in contact with a protective gas.